An observation of interest for those who track HDD's

 
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Post by lsayre » Fri. Nov. 06, 2020 7:10 am

The old school method of computing a days average temperature has been to simply add the days high temperature and the days low temperature and divide by two.

A better method is to mathematically integrate the temperature over small units of time by which to achieve a high precision average temperature for the day.

But for awhile now I've been spreadsheet tracking the two methods, and I've observed that for heating season months the integrated daily average temperature seems to be rather consistently on average 0.4 degrees lower than the result achieved via the simple old school method.

I can tentatively conclude from this that a typical heating season days actual average temperature will be very close to:

(Days High + Day's Low)/2 - 0.4 = days average temperature

For those who do not have access to integrated daily average temperature data for your area, this seems to be an excellent compromise improvement by which to better determine a days average temperature.


 
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Post by nepacoal » Fri. Nov. 06, 2020 7:47 am

Glad you did this... It's always bothered me on those days when a front came through at the beginning or end of a 24 hour period. The average temp using just the high low would be skewed... I might start a spreadsheet to use this method. Thanks.

 
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Post by Lightning » Fri. Nov. 06, 2020 7:53 am

I agree.. it only makes sense that you would need to subtract something since solar heating only happens for about 1/3 of the day in the winter months instead of half.

 
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Post by lsayre » Fri. Nov. 06, 2020 8:05 am

The data I used is from all of April, May, September, October, and partial November. I wonder if the subtraction factor will grow larger than 0.4 degrees in the depths of real winter? Stay tuned....

 
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Post by Lightning » Fri. Nov. 06, 2020 8:15 am

I'm thinking it will just for the reason I stated above. ;)

 
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Post by lsayre » Fri. Nov. 06, 2020 8:52 am

Lightning wrote:
Fri. Nov. 06, 2020 8:15 am
I'm thinking it will just for the reason I stated above. ;)
I have that inkling also.

 
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Post by lsayre » Fri. Nov. 06, 2020 9:00 am

nepacoal wrote:
Fri. Nov. 06, 2020 7:47 am
Glad you did this... It's always bothered me on those days when a front came through at the beginning or end of a 24 hour period. The average temp using just the high low would be skewed... I might start a spreadsheet to use this method. Thanks.
0.4 degrees is an average of the monthly averages. It was actually 0.43 degrees. On a daily basis the data is more scattered between integrated and simple, but I've never observed more than 2.9 degrees of daily deviation between the methods so far.


 
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Post by lsayre » Fri. Nov. 06, 2020 9:23 am

If you can find it, a local brand called 'Walnut Creek' (most commonly found at Amish and Mennonite bulk food stores, but also found in some of the big box stores around here) is pretty good Braunschweiger. They hail out of the city of 'Walnut Creek, OH.'

https://www.walnutcreekfoods.com/products/deli-me ... er-wc-4-lb

http://cometowalnutcreekohio.com/wp-content/uploa ... p-2019.pdf

 
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Post by lsayre » Thu. Nov. 19, 2020 9:54 am

So far, in November to date the integrated daily average temperature is about 0.87 degrees lower than for simply adding the high and low of the day and dividing by 2. It may indeed be that the colder it gets, and the less hours of sunshine, the greater this gap will get. But only time will tell.

 
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Post by Lightning » Thu. Nov. 19, 2020 2:52 pm

Are you using Weather Underground data?

 
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Post by lsayre » Thu. Nov. 19, 2020 3:11 pm

Lightning wrote:
Thu. Nov. 19, 2020 2:52 pm
Are you using Weather Underground data?
Yes

 
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Post by Lightning » Thu. Nov. 19, 2020 7:10 pm

lsayre wrote:
Thu. Nov. 19, 2020 3:11 pm
Yes
From what I understand, they average the hourly readings to get their daily mean?

 
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Post by lsayre » Thu. Nov. 19, 2020 7:33 pm

Lightning wrote:
Thu. Nov. 19, 2020 7:10 pm
From what I understand, they average the hourly readings to get their daily mean?
I guess I initially thought they were doing a much better daily temperature data integration job than that. But even so, it's 24 daily temperature data points vs. 2 daily temperature data points. So it has to be way more accurate.

Better integration would be by the minute. The average of 1,440 daily temperature data points.

 
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Post by lsayre » Tue. Dec. 01, 2020 8:09 am

The final differential between (high + low)/2 and 24 point integration for November was 0.54 degrees. Integration averaged to 0.54 degrees lower than the simple method.

 
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Post by lsayre » Fri. Dec. 18, 2020 9:53 am

The differential 'to date' between (high + low)/2 and 24 point integration for December is exactly 0.5 degrees. It's beginning to look like a ballpark 0.5 degrees of difference will likely hold up.

Therefore:
(high + low)/2 - 0.5 ~= the integrated 'actual' average daily temperature


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